This invention relates to a method of monitoring temperature of a human body and devices for achieving same and, more particularly, to such a method and device which monitors the internal core temperature of a person undergoing continuous medical observation.
Frequently, during surgical and other medical procedures related to humans and animals, there is a need for continuous monitoring of the body core temperature. Core temperature here means temperature of blood flowing around the brain and other vital internal organs. It has been recognized long time ago that the core temperature is an accurate parameter for assessing the physiological functions and metabolic activity of a body.
Traditionally, there are several known devices for continuous assessing body temperature of a patient. All these devices primarily differ by the measurement site. Specifically, they are 1) an esophageal probe, 2) a rectal probe, 3) skin temperature probes, and 4) an intermittent instant ear thermometers, often called tympanic. The last device presently can not provide a continuous monitoring. The first two devices yield accuracy well acceptable for the diagnostic and monitoring purposes and account for the majority of present temperature recordings. These traditional devices are invasive, may require sterile probes (esophageal), often inconvenient and, as a rule, not acceptable for patients outside the operating rooms. A skin temperature monitoring is used sporadically as it is more influenced by the ambient temperature. The need for an easy, inexpensive, accurate, and comfortable way of continuous temperature monitoring is substantial.
It has been recognized long time ago that the tympanic region of the ear canal follows the body core temperature with high fidelity. The region includes the tympanic membrane and the adjacent walls of the ear canal. This premise has been the basis for the tympanic thermometers, including both the contact and non-contact (infrared) types. An example of a contact transducer is a miniature thermistor (produced, for example, by Vital Signs, Inc.) that is positioned directly on the surface of a tympanic membrane with the connecting wires secured inside the ear canal. Generally, this can be performed only on an anesthetized patient with a risk of damaging the tympanic membrane and thus is rarely used in medical practice. Another example is a contact temperature transducer that is incorporated into an ear plug (U.S. Pat. No. 3,274,994). Examples of continuous noncontact optical infrared probes are given in U.S. Pat. Nos. 3,282,106 and 3,581,570.
Contact detectors are much simpler than noncontact, but they both suffer from the same effectxe2x80x94difficulty of a reliable placement inside the ear canal. Placement of a contact temperature transducer inside the ear canal without a reliable securing of it at any specific position may cause a high inaccuracy in measurement, due to unpredictable effects of the ambient temperature and placement technique of the probe. An attempt to incorporate a temperature transducer into an ear plug similar to a hearing aid device is exemplified by U.S. Pat. No. 5,333,622 issued to Casali, et al. Yet, the teaching does not resolve the accuracy problem due to heat loss. Besides, such a probe requires an individual tailoring of its shape. It should be noted that besides a temperature measurement, there are some other types of measurements that may require a secure adaptive positioning of a transducer inside a body cavity.
Therefore, it is a goal of this invention to produce a sensing device that can be positioned securely and reliably in a body cavity;
Another goal of the invention is to make an ear temperature transducer with a contact probe that is automatically secured at an ear canal wall;
It is another goal of this invention to produce an ear temperature transducer that tracks the core temperature with high fidelity;
It is another goal of this invention to make an ear temperature transducer that is less influenced by the ambient temperature;
It is another goal to provide an ear temperature transducer that doesn""t cause a discomfort for a patient and can remain in the ear canal for a prolonged time;
The goals of this invention is achieved by the novel ear temperature detector. The detector is comprised of an ear plug carrying the temperature sensing device wherein the sensing device is characterized by its increased thermal coupling to a wall of an ear canal and decreased coupling to the environment. This is attained by pre-shaping the plug into a smaller size and allowing to change its shape upon the insertion, until the sensing device is clamped between the plug and the skin. To correct for a thermal gradient across the ear plug, the plug has low thermal conductivity and its external temperature is monitored. Alternatively, temperature of the external portion of the plug is actively controlled by a heater attached to the plug. The heater forms a thermal shield around the temperature sensing device, thus negating a thermal gradient across the plug.